Shares Repurchased	12 Months Ended
Dec. 31, 2017
Equity [Abstract]
Shares Repurchased	17. Shares Repurchased On October 29, 2014, the Company’s Board of Directors authorized a three-year share repurchase program of up to $100,000. On April 27, 2016, the Board of Directors approved a $60,000 increase to the Company’s share repurchase program and extended the term through April 27, 2019. Included under this program are purchases to offset future equity grants made under the Company’s equity plans and are made in open market or privately negotiated transactions. This authority may be exercised from time to time and in such amounts as market conditions warrant, and subject to regulatory considerations. The timing and actual number of shares repurchased depends on a variety of factors including price, corporate and regulatory requirements, market conditions and other corporate liquidity requirements and priorities. The repurchase program may be suspended or terminated at any time without prior notice. Shares repurchased under this program are returned to the status of authorized and unissued on the Company’s books and records. If the Company’s pending acquisition of ETFS is ultimately completed, its ability to freely repurchase shares of its common stock will be restricted. Under the terms of the credit agreement governing the credit facilities the Company plans to use to partially finance the acquisition of ETFS, share repurchases only will be permitted to the extent the Company complies with a leverage test and no event of default (as defined in the credit agreement) has occurred and is continuing at the time the share repurchase is made. However, the Company’s ability to purchase shares of its common stock withheld pursuant to the terms of equity awards granted to employees to satisfy tax withholding obligations will not be restricted. During the years ended December 31, 2017, 2016 and 2015, the Company repurchased 697,664 shares, 3,778,932 shares and 1,190,356 shares of its common stock, respectively, under this program for an aggregate cost of $7,891, $39,379 and $24,116, respectively. Shares repurchased under this program were returned to the status of authorized and unissued on the Company’s books and records. As of December 31, 2017, $88,614 remains under this program for future purchases.

17. Shares Repurchased

On October 29, 2014, the Company’s Board of Directors authorized a three-year share repurchase program of up to $100,000. On April 27, 2016, the Board of Directors approved a $60,000 increase to the Company’s share repurchase program and extended the term through April 27, 2019. Included under this program are purchases to offset future equity grants made under the Company’s equity plans and are made in open market or privately negotiated transactions. This authority may be exercised from time to time and in such amounts as market conditions warrant, and subject to regulatory considerations. The timing and actual number of shares repurchased depends on a variety of factors including price, corporate and regulatory requirements, market conditions and other corporate liquidity requirements and priorities. The repurchase program may be suspended or terminated at any time without prior notice. Shares repurchased under this program are returned to the status of authorized and unissued on the Company’s books and records.

If the Company’s pending acquisition of ETFS is ultimately completed, its ability to freely repurchase shares of its common stock will be restricted. Under the terms of the credit agreement governing the credit facilities the Company plans to use to partially finance the acquisition of ETFS, share repurchases only will be permitted to the extent the Company complies with a leverage test and no event of default (as defined in the credit agreement) has occurred and is continuing at the time the share repurchase is made. However, the Company’s ability to purchase shares of its common stock withheld pursuant to the terms of equity awards granted to employees to satisfy tax withholding obligations will not be restricted.

During the years ended December 31, 2017, 2016 and 2015, the Company repurchased 697,664 shares, 3,778,932 shares and 1,190,356 shares of its common stock, respectively, under this program for an aggregate cost of $7,891, $39,379 and $24,116, respectively. Shares repurchased under this program were returned to the status of authorized and unissued on the Company’s books and records.

As of December 31, 2017, $88,614 remains under this program for future purchases.